BUILDING. 
breadth of the foundation will be as the 
area of the vertical section passing through 
the line on which the breadth is measured 
thus for example, suppose a wall 40 feet high, 
g feet thick, to have a sufficient foundation 
at 3 feet in breadth, what should be the 
breadth of a foundation of a wall 60 feet 
high, gi feet thick : by proportion it will be 
40 X 2 : 3 60 X 52^ : the ans, = feet. This 
c.alculation will give the breadth of the 
foundation of the required wall, equal to the 
breadth of the insisting wall itself ; when 
the height of the required wall is equal to 
the ratio, which is the first term 40 X 2 = 80, 
divided by the secpnd terra 3, that is 
5^^ z= g6^. Thus a wall of 26§ feet, would 
have the breadth of its foundation, equal to 
its thickness above the foundation, aud less 
than gtif feet, would have a tliinner founda- 
tion, than even the superstructure. But 
though the calculation in this case gives the 
foundation less breadth than the thickness 
of its superstructure, it must be considered 
that it only calculates the true breadth of 
surface that should be opposed to the 
ground, in order to prevent the wall from 
penetration by its weight ; though the rule 
gives all the breadth that is necessary, on 
accoimt of the weight of the insisting wall, 
yet the breadth of the substructure should 
always be greater than that of the super- 
structure ; as it will stand more firmly on 
its base when affected by lateral pressure, 
and be less liable to rock by the blowing of 
heavy winds. The least breadth that is 
commonly giyen to the substructure of 
stone walls is one foot thicker than the su- 
perstructure. In damp foundations the 
superstructure should always be separated 
from the substructure by lead, tarred paper, 
or other means. 
Stone Arch. Stone arch is a number of 
stones so arranged that, in consequence of 
their pressure upon one another and upon 
their support^, they may be suspended over 
a hollow space ; every interior stone being 
such that if a plummet be depended by a 
line from any point in that stone, the line 
will fall witiiin the hollow space. 
Stone arches are generally hollow below, 
and concave towards that hollow. The in- 
terior stones onght to be truncated wedges, 
a. d their faces, which form the intrudes, of 
less dimensions than tlie upper opposite sur- 
faces which form the extrado^; so that 
when any stone endeavours to descend 
through the aperture which surrounds it, it 
w'ill be prevented by the dimensions of the 
lower part of the aperture being less thap 
those of the top of the stone which has t«> 
fall through it. 
Wedge-like stones forming an aroh are 
arch stones. 
The joints between the arch stones are 
called sommerings. 
Tlie support or supports of an arch are 
called the reins of that arch. 
When the support or supports of an arch 
are stone walls, the upper course or courses 
on which the beds of the extreme arch 
stones rest, are called the imposts. 
Spring course or chaptrels of the arch, 
and beds themselves, are called the hut- 
ments or abutmeuts, or spring beds, or 
skew backs of the arch. 
When an arch is either recessed in any 
piece of masonry, or forms the head of an 
aperture through tliat piece of masonry, the 
arch stones which are common to the intra- 
dos and to the face of the masonry ; are 
called voussoirs, and the middle voussoir is 
called the key stone. 
Stone arches are used for a variety of 
purposes, in supporting different parts of a 
building, over apertures when the apertures 
are too wide for lintelling, and over a 
yvooden or stone lintels, to assist in sup- 
porting the superincumbent building. 
Arches are also used to prop the sides of 
a building, and in soft foundations inverte4 
arches are used, between narrovy piers, to 
prevent the pier from penetrating, by op- 
posing a greater surface of resistance to the 
ground. 
Floors and roofs are frequently supported 
with arches, in order to render the building 
niore secure from fire. 
Arches employed for several of these pur- 
poses have been denominated as follows ; 
those over wooden lintels have been called 
occult discharging arches, or arches of dis- 
charge ; those used to prop the sides of ^ 
building are called arch boutants, or flying 
buttresses; and those over apertures, the 
intrados of which are horizontal planes, 
have been absurdly called straight arches ; 
it is only for the property of its radiating 
joints this last is called an arch. 
Because the courses in every kind of 
masonry ought to be horizontal, or the 
nearest position to it that the nature of the 
arch will admit of ; in stone arching, it fol- 
lows that when the intrados is a rotative 
figure with a vertical axis, the coursing joints 
will be conic surfaces, and their intersec- 
tions upon the intrados horizontal circles, 
and the transverse joints will be planer 
sending to the axis : when the axis is hofizop- 
